Various reinforcing materials have long been used to increase the strength of rubber articles, including tires, hoses, and the like. Metallic wire, and in particular brass coated steel wire is commonly used as reinforcement. A primary requirement for effective reinforcement is that the reinforcing material remain tightly bonded to the rubber. Good adhesion is difficult to achieve where, as in the case of a tire, the article is subject to continuous flexing and exposure to high temperatures during use. High initial adhesion may be obtained by providing good mechanical contact between the rubber and the wire during cure but, upon aging and use of the article, the bond is often weakened or is lost completely, resulting in premature failure. To prevent this, adhesion promoters are often used which can maintain a high level of adhesion between the rubber and metal. The promoters are commonly added to the rubber compounding recipe prior to cure. The present invention provides for a novel wire adhesion promoter which is the reaction product of a substituted melamine and a phenol or alkyl substituted phenol. The product, a resin, is then neutralized, purified and added to the uncured rubber during compounding in a conventional manner.
U.S. Pat. No. 3,517,722 to Endter, et al, discloses rubber modified with a resin formed in situ from the reaction of a methylene donor and a methylene acceptor. The donor includes a substituted melamine while the acceptor may be m-aminophenol (MAP) or a resorcinol. This patent differs from the present invention in that the reaction in the former is carried out in situ, has no neutralization or purification step, and a phenol or alkyl substituted phenol is not used.
U.S. Pat. Nos. 4,189,421 and 3,904,623 to Shay, et al, refer to the use of the reaction product of a phenolic and a triazine compound as a crosslinking agent in powder coatings, for example, polyesters. There is no teaching or suggestion of the use of such a reaction product as an adhesion promoter between rubber and metal. Thus, these patents are not pertinent.